The invention relates to a pedal displacement sensor.
In motor vehicles, it is customary practice to arrange within the region of a pedal one or more electric switches that determine the pedal position and deliver corresponding control signals. For example, some agricultural tractors have right and left brake pedals which can be operated separately in order to drive through tight curves. Each brake pedal acts directly upon one brake cylinder. The trigger element of a brake light switch, which is actuated when the pedal is actuated and delivers an electrical signal to the brake light, is arranged within the travel range of each pedal. In this case, the actuation point is frequently subject to a relatively marked hysteresis that is acceptable for the actuation of brake lights.
It would be desirable to make functions of the vehicle other than the brake lights, e.g., the addition of a front wheel drive and the actuation of a differential lock, dependent on the position of the brake pedal. However, these functions make it necessary to have a precise relationship between pedal displacement and switch activation.
In U.S. Pat. No. 5,920,048, it is proposed to determine the position of the accelerator pedal and the brake pedal of an electric vehicle with devices in which an electric switch and an adjustable resistor are arranged in a housing. A shaft extends through the housing and is connected to the accelerator pedal or the brake pedal and turns in accordance with the pedal movement. The shaft is connected to a pivoted actuating element which acts upon the switch when the shaft is turned. A wiper is mounted on the actuating element and moves over a resistive coating when the shaft is turned. This causes the resistance of an electric circuit to change such that a signal corresponding to the pedal position is generated. This device is relatively complicated because it requires a shaft that is connected to a pedal, and it may be difficult to adapt it to existing pedal arrangements. Due to the mechanical brush contacts, this device is also relatively susceptible to defects, and is not very accurate.
Accordingly, an object of this invention is to provide a pedal displacement sensor of the type initially mentioned that eliminates the aforementioned problems.
A further object of the invention is to provide such a pedal displacement sensor which provides a reliable determination of the pedal position with reproducible, largely hysteresis-free switching points.
A further object of the invention is to provide such a pedal displacement sensor which has a simple design, and which is simple to install and does not require complicated adaptations or subsequent adjustments.
These and other objects are achieved by the present invention, wherein a pedal displacement sensor has a housing with an opening through which extends a portion of a pivoting actuating lever. A portion of the lever outside the housing operatively engages a brake pedal, so that the pedal acts directly upon the lever, i.e., without intermediate components such as shafts, levers and the like. As a result, the risk of jamming or seizing is, in contrast to linear movements, significantly reduced, and hysteresis effects are largely avoided.
The pedal displacement sensor is preferably separately manufactured in the form of a simple pre-adjusted component and can be mounted in the vicinity of the pedal lever with simple means, e.g., screw connections, without requiring adaptation measures and subsequent adjustments. Special precautions for the transmission of power between the pedal lever and the actuating lever of the pedal displacement sensor are not required.
Preferably, the actuating lever is an angle lever having a first arm and a second arm joined together to form a bend. The first arm is rotatably supported, and the second arm projects out of the opening in the housing. The second arm has an end face which is subjected to a pedal force which acts essentially perpendicularly upon the end face.
The housing is preferably compact and stable. The housing walls, in particular, the lead-throughs for electrical lines, are hermetically sealed so that environmental influences, e.g., dust and splash water, do not impair the function of the pedal displacement sensor. Within the region of the opening in the housing, the housing is sealed relative to the actuating lever, in particular, relative to the end of its second arm, by a flexible rubber collar.
The actuating element of the switch is preferably arranged in the vicinity of the bend of the angle lever and lies approximately opposite to the end face of the second arm. The greatest excursion of the angle lever occurs in the vicinity of the bend, so that the switching element is able to respond to actuations of the pedal lever in a relatively precise fashion. The switching element preferably consists of a commercially available microswitch with a pushbutton.
Preferably, a spring tongue is mounted on the actuating lever, with the free end of the spring tongue acting upon the actuating element of the switch. This prevents the entire force exerted upon the actuating lever from being transmitted to the actuating element of the switch and avoids damage to the switching element or variations in its switching point. Consequently, one preferred additional development of the invention proposes that the actuating lever does not act directly upon the actuating element. A limit stop may be integrated into the contour of the housing and arranged in the travel path of the spring tongue in order to limit its excursion.
A spring, such as helical compression spring, urges the actuating lever away from a position that corresponds to the position of the depressed pedal (e.g., the braking position), with the actuating element of the switching element not being actuated by the actuating lever in this position. The spring preferably engages the lever near the bend between the two arms and presses the actuating lever in the direction opposite to the force occurring during pedal actuation.
The actuating lever acts upon a measurement device or transducer which generates an electrical signal representing the rotational position of the actuating lever, and thus the position of the pedal. Preferably, the transducer is a non-contacting transducer, such as a Hall sensor with a magnet. A permanent magnet that moves with the actuating lever is preferably arranged on the actuating lever, with the Hall sensor being fixed in the housing within the magnetic field of the permanent magnet. When the permanent magnet is moved due to actuation of the actuating lever, the magnetic flux within the region of the Hall sensor, and consequently its output signal, are changed. Preferably, the permanent magnet is mounted on the actuating lever near to its rotational axis, and is aligned so that an axis which connects the magnetic north pole and the magnetic south pole extends approximately perpendicular to the rotational axis of the actuating lever.
In order to achieve a largely linear correlation between the pedal position, and consequently the rotational position of the actuating lever, on the one hand, and the sensor signal on the other hand, one particularly advantageous arrangement of the Hall sensor is characterized by the fact that the Hall sensor is arranged to be approximately in the mid-plane extending between the magnetic north pole and the magnetic south pole of the permanent magnet. In this arrangement, the permanent magnet moves almost linearly along its north-south alignment past the Hall sensor when the actuating lever is turned. Consequently, the Hall sensor signal is approximately proportional to the rotational position of the permanent magnet and thus is proportional to the excursion of the actuating lever and the pedal displacement.
In motor vehicles which have two brake independently operable brake pedals, the pedal displacement sensor preferably includes two rotatable actuating levers in a single sealed housing, each corresponding to one of the brake pedals. A switching element and a transducer is assigned to each of the two actuating levers.
In order to allow a direct evaluation of the signals of the switching elements and transducers, it is advantageous to arrange additional electrical or electronic components in the housing of the pedal displacement sensor, such as relays and/or printed circuit boards with electrical components. This reduces the requirements with respect to cable harnesses and plug connections.
Preferably, the pedal displacement sensor is a pre-assembled module, in which all components that determine the pedal position are accommodated in a hermetically sealed housing, and which can be manufactured and adjusted so that it is ready for use by a component supplier. Then, during final assembly of the motor vehicle, the module can be installed in the vicinity of the pedal in the form of a unit, without requiring any subsequent adjustments.